1. Field of the Invention
This invention relates to optical devices and more particularly to an assembly for optical devices comprising two components which are required to be positioned with respect to each other so as to provide for the efficient transmission of optical signals from one to the other.
2. Related Art
The invention has an important application in the manufacture of optical communications apparatus where, for example, accurate and stable relative positioning is required between two components. For the present purposes it is convenient to identify one of the components as a source component and the other as a receptor component. It is a common requirement in optical communications to juxtapose these so that the receptor component is accurately located so as to acquire optical signals provided by the source component. For example, one of the components may comprise a passive optical device in the form of optical fibre waveguide, and the other component an active optical device such as a laser, photo diode. Accurate and stable relative positioning between the source component and the receptor component is required to ensure optimal and stable optical alignment of the optical devices. Similarly, such accurate and stable relative positioning may be required between two components comprising active devices or two components comprising passive devices.
It is now convenient to identify the various forms of optical devices which source components and receptor components commonly comprise.
The source component may comprise a signal generator, e.g. a semiconductor device which converts electric power into an optical signal. Examples of such semiconductor devices include light emitting diodes (LED), edge emitting LEDs (ELED), and a wide variety of semiconductor lasers. Many of these devices comprise waveguiding structures. The signal generator often provides a divergent beam which is inconvenient for forming an optical connection. In such circumstances it is usual for the source component to include lenses which either collimate the beam or to cause it to converge to a focus. The source component may also comprise a passive device, e.g. a passive optical waveguiding structure such as an optical fibre.
The receptor component may be an optical detector, e.g. a semiconductor device which converts an optical signal into an electrical signal. Examples of such devices include photo diodes and PIN diodes. The receptor component may also comprise a waveguiding structure, e.g. a passive waveguiding structure such as an optical fibre, which is adapted to receive an optical signal from the source component for onward transmission to a receiving station.
It should be noted that passive waveguiding structures can be utilised either in the receptor component (e.g. an optical fibre for transmitting the output of an optical transmitter) or in the source component (e.g. an optical fibre terminating at an optical receiver).
Optical isolators are a well known example of passive optical components of the type in which a waveguide structure need not be employed.
It has been mentioned above that one of the components may comprise a waveguiding structure. In some cases the end of an external waveguiding device may be permanently comprised in the component, e.g. a fibre tail may be permanently located for the transmission of the optical signal. However, optical technology includes a wide range of connectors, e.g. connectors in which a plug, connected to a first fibre, is inserted into a socket, connected to a second fibre. In other embodiments of the invention the waveguiding structure takes the form of a plug or a socket which is adapted to connect to an external waveguiding device. When the connection is completed the external waveguiding device is operatively connected to the internal device. The location of the plug or the socket therefore (indirectly) locates the external waveguiding device and this is an important embodiment for optical devices in accordance with the invention.
It is emphasised that, in all the cases mentioned above, a satisfactory performance of assembly depends upon the accurate relative location of the two components whatever form these components may take. It will also be appreciated that, whatever the optical function, the components often comprise similar, or identical cases, and, therefore, the mechanical problem of the assembly of the devices is independent of the optical function.
Typically, the optical tolerances are less than .+-.3 .mu.m and preferably less than .+-.1 .mu.m. In the case where one of the components includes a socket or plug for making connections to external waveguides, e.g. fibre, it will be apparent that there is a variability in the overall performance of the assembly because the plug does not always go into exactly the same position in its socket. The plug and socket are designed .so that this error is small but it is necessary that the combined error be kept within the tolerances mentioned above. This means that the relative location of the two components is always subject to tight tolerances which must be maintained within the lifetime of the device.
The basic method of assembling the devices is well established. The source component is activated and the relative positions of the source component and the receptor component are experimentally adjusted until the receptor component acquires maximum output. With the two components in this optimum configuration, they are secured by the application of adhesive. Many jigs are available which allow this process to be carried out and the jigs are capable of holding the two components in accurate juxtaposition so long as both remain within the jig. It has, however, been observed that the performance of the assembly deteriorates more rapidly than the lifetimes of its individual components would imply. It is an object of this invention to reduce the rate of this deterioration.